Screen supply capacitor and bias caps

[olNick]

Hi again,


Two q's
Been slowly recapping my VT-22 distortion model, as per my previous thread.

I have a 50uf, 500V x 4 multi-can cap replacing C304, A,B,C...

1. Can I use the fourth section to replace C302B, the screen supply cap? Or should I use a separate cap?

I ask because the screen supply seems to be active only when the standby switch is activated (seems like it lifts the ground when inactive). Basically trying to avoid smoke...

2. Since the life of these amps hangs on the bias caps and resistors
C207 and C208(in the distortion model 10uf/100V) what type/better caps and resistors can I use here instead of the electrolytics?

tia,
Nick

[olNick]

Bump....

[Hangman]

Hi Nick,
No, I wouldn't recommend that. Unfortunately the Standby switch works by disconnecting the plate and screen supply gnd. if you use that cap for the screen supply, the gnd will permanently be connected. The standby switch would still work for the plate supply, but not the screen supply (and bias supply). I'd be concerned that the screen would start acting like plate, since there was bias voltage, and the cathodes of the power tubes would still be connected to gnd.

[olNick]

Thanx Steve, I'm using a separate cap here.

Hi Nick,
No, I wouldn't recommend that. Unfortunately the Standby switch works by disconnecting the plate and screen supply gnd. if you use that cap for the screen supply, the gnd will permanently be connected. The standby switch would still work for the plate supply, but not the screen supply (and bias supply). I'd be concerned that the screen would start acting like plate, since there was bias voltage, and the cathodes of the power tubes would still be connected to gnd.